A shaft seal for sealing a rotary shaft usually comprises an outer flange area, with which the seal can be inserted, for example, into a housing of a bearing for the shaft, and a sealing lip which is arranged inside the flange area and which provides a sealing action by bearing on the surface of the rotary shaft. To ensure that the sealing lip is pressed with sufficient pressing force onto the shaft, an annular spring is normally provided on an outer face of the sealing lip, which annular spring yields the necessary pressing force. A shaft seal of the stated type is also referred to as a rotary shaft seal.
DE 10 2010 041 611 A1 discloses a rotary shaft seal of this kind, which has an elastomer body with a substantially U-shaped cross section, with a sealing lip arranged on the inner passage side of the seal, and with an outer flange area. The flange area has a clamping surface and a sealing surface for respectively clamping and sealing the rotary shaft seal in a flange of a structural part. On the inner side of the sealing lip, a clamping ring is provided, which serves to press the sealing lip onto the shaft.
As clamping ring or spring, it is customary to use helical tension springs or garter springs, which ensure a sufficient pressing force and a sufficient deformability of the sealing lip. To maintain the radial force of the spring even in chemically aggressive media or in media containing solid particles of dirt, it has been proposed in patent specification DE 37 02 913 C1 that the running surface of the sealing lip and the helical tension ring, bearing on the outside of the sealing lip, are protected by a ring of low-friction plastic which has an approximately U-shaped cross section and is pushed over the sealing lip including the helical tension spring.
It is also known for a spring of a shaft seal to be embedded in the material from which the seal is made. However, the mechanical properties of the spring are disadvantageously altered in this way. In particular, a seal of this kind is very stiff and, with respect to the manufacturing tolerances of the seal and to the tolerances of the shaft that is to be sealed, does not permit precise adjustment of the contact pressure of the sealing lip. Potting the seal with silicone is also disadvantageous, particularly because of the danger of cracks forming.
Particularly in medical appliances in which a rotary shaft has to be sealed, it is particularly important that the seal is able to provide reliable sealing with compensation of possible tolerances. Moreover, in medical uses, for example in a surgical handpiece with a rotary shaft, the problem arises that the shaft seal, which is generally arranged on the outwardly exposed side of the seal, may come into contact with tissue, blood or other body fluids. Before repeat use of the handpiece, the seal has to be cleaned and sterilized. Therefore, particular demands are placed on the cleanability and on the stability and leaktightness of the shaft seal even under conditions of increased heat and pressure which occur during sterilization.